Lead isotope ratios in urban road runoff.

Lead isotopic analyses of road runoff and airborne particulate matter have been carried out to elucidate sources of lead pollution at urban and suburban sites. While lead is often observed in road runoff in suspended form, suspended particle size had no relation to the lead isotopic distribution, as a result of comparison between runoff samples with total suspended solids and those with minute particles passed through a 75 microm sieve. Lead isotope ratios in airborne particulate matter in urban areas fell within a wider range than those in road runoff. Since there was little difference of the ratios between a heavy traffic-flow site and residential sites, airborne lead derived from vehicle exhaust was found to make little contribution to the contamination of road runoff. On the other hand, the ratios in road runoff at a suburban site showed the same range as those at an urban site. Lead in road runoff was therefore suggested to be produced on site by traffic related substances, such as tire wear, other than vehicle exhaust.     

An alternate approach for transient flow modeling in urban drainage systems

Implementing control structures such as gates at suitable locations in the urban drainage network enables its improved utility by actively controlling and optimizing the flow during a flood event. The successful operation of the control structure is fully governed by the suitability and efficiency of the control strategy adopted, which in turn depends on the response characteristics of the urban drainage system under different flow conditions. For an extreme rainfall event, it is necessary to model the transient flow in the urban drainage system. However, such an exercise is mostly restricted by the limited data and lack of in-depth survey of urban drainage systems in most of the developing countries like India. Taking this into consideration, an alternate approach has been presented in this paper for modeling the transient flow in the urban drainage system under limited data availability. The results obtained have also been compared with the finite difference model using four-point implicit scheme in time domain. The developed model can be used for the computation of temporal distribution of water surface profile with special consideration of lateral inflow. The application has been demonstrated by applying it to a representative catchment in Mumbai, India.     

Real-Time Operation of Pumping Systems for Urban Flood Mitigation: Single-Period vs. Multi-Period Optimization

To reduce flood risk in urban regions, it is important to optimize the performance of operational elements such as gates and pumps. This paper compares the performances of two approaches of multi-period and single-period simulation-optimization that are used to derive real-time control policies for operating urban drainage systems. The EPA storm water management model (SWMM), converting real-time rainfall data to surface runoff at network control points, i.e. pump stations, is linked to the particle swarm optimization (PSO) algorithm, evaluating the system operation performance measure (objective function) for different sets of control policies. A prototype network in a portion of the Seoul urban drainage system is used to investigate the efficiency of the proposed approaches. Results justify the high efficiency of multi-period optimization, leading to 32 and 29% average reductions in peak water level violations from a pre-defined permissible threshold at target points and the number of pump switches, respectively, in comparison with the online single-period optimization. The myopic policies derived by single-period optimization are not reliable, and in some cases, they even perform worse than ad-hoc policies applied by system operators based on their past experiences.     

The efficiency of asset management strategies to reduce urban flood risk

In this study, three asset management strategies were compared with respect to their efficiency to reduce flood risk. Data from call centres at two municipalities were used to quantify urban flood risks associated with three causes of urban flooding: gully pot blockage, sewer pipe blockage and sewer overloading. The efficiency of three flood reduction strategies was assessed based on their effect on the causes contributing to flood risk. The sensitivity of the results to uncertainty in the data source, citizens' calls, was analysed through incorporation of uncertainty ranges taken from customer complaint literature. Based on the available data it could be shown that increasing gully pot blockage is the most efficient action to reduce flood risk, given data uncertainty. If differences between cause incidences are large, as in the presented case study, call data are sufficient to decide how flood risk can be most efficiently reduced. According to the results of this analysis, enlargement of sewer pipes is not an efficient strategy to reduce flood risk, because flood risk associated with sewer overloading is small compared to other failure mechanisms.     

杨房沟水电站上铺子沟泥石流治理工程设计

上铺子沟位于杨房沟水电站坝址下游约2.6 km,为沟谷降雨型低频大型黏性泥石流沟。沟水及泥石流发育规模均较大,沟内布置有弃渣场,总量达1 150万m3,该沟的泥石流防治对电站的建设运行有重要影响。根据该工程地形地质及泥石流特点,确定"以排为主,拦粗排细"的设计理念,采用沟水截排处理和泥石流防护相结合的防护方案,布设格栅拦挡坝、挡水坝以及排导槽等设施,简化了施工难度,确保了上铺子沟弃渣场在施工期及运行期的安全。     

Modeling of anaerobic treatment of wastewater in ponds.

A mathematical model to simulate the performance of anaerobic ponds was developed incorporating both settling of particulate components and the biological anaerobic digestion process. The biological activity includes solubilization of particulate organic matter; methanogenesis and the sulphate reduction process. The model considers that an anaerobic pond comprises a series of equal size columns. Each column has three compartments viz. liquid layer, active sediment layer and inert sediment layer. The existence of organic matter and sulphate removal mechanisms both in the bulk as well as sediment layer of the ponds and the exchange of the soluble components between the layers has been included in the model. The model was transferred to a computer program using VisSim Basic software. The model was verified by comparing simulated results with full-scale as well as with laboratory-scale anaerobic pond performance data. A good agreement between the simulated and the observed pond performance was achieved.     

絮团与颗粒不等速沉降碰撞研究

絮团和单个颗粒的碰撞、粘结规律对于深入理解粘性泥沙不等速沉降引起的絮凝具有重要意义。在暂不考虑絮团与颗粒间相互作用力的条件下,用不同密度球形颗粒近似描述絮团,利用格子Boltzmann方法模拟了不同密度絮团和单个颗粒静水沉降过程,分析了絮团和颗粒相对运动轨迹和碰撞效率。模拟结果表明,絮团和单个颗粒不等速沉降碰撞过程中,当较大粒径的絮团沉降速度快但密度较小时,单个颗粒相对于絮团运动可能形成封闭轨迹,絮团和颗粒间粘结概率几乎为零,絮团很难通过捕捉单个颗粒而形成更大絮团。     

重力场中的粒子在沉降过程中的捕捉和再分离过程

本文对重力场中的粒子在沉降过程中的捕捉和再分离过程进行了理论上的研究。为了数学上处理方便，考虑圆球粒子在黏性流体中作低雷诺数运动。使用调和函数和双调和函数在不同坐标系中的变换关系和作者提出的扩展的连续反射方法，根据Lamb给出的低雷诺数流动的基本解表达式和线性方程的叠加原理，本文构造出了围绕两个球形粒子流动的完全解和在准静态条件下沉降粒子所受到的水动力和力矩的精确解。结合刚体力学中处理约束问题的方法和摩擦理论使得本文理论上证实了界面摩擦力是Stokes方程对称性预测失效的原因，并且确定了运动粒子在界面上的两种运动类型（纯滚动及其滚动伴随滑动）和范围，从而这使得本文可以描述粒子在沉降讨程中的捕捉和再分离过程。     

Particles under stress

The complex nature of particulate matter in natural water resources and in waste waters is characterized by the heterogeneous distribution of particle size, shape, density, and shear strength. Among these parameters, floc strength is most important in the last stages of flocculation. Experimental data on floc strength based on different methods are assessed and correlated with shear gradients in different aquatic environments. The analysis of turbulent motion reveals that the energy which affects particle agglomerates is only a small portion of the totally dissipated energy. Among the different flow fields in turbulent motion, converging/diverging flow cause strain forces which prove to be critical with respect to floc rupture. Model calculations of the surface forces on ellipsoidal particles in pure shear and strain flow fields and corresponding experiments confirm the importance of converging flow. A comparison of modeled and measured rupture forces allows to establish relationships between floc size, strain and shear rates and resulting surface forces leading to probable floc break-up. Flocs of appreciable size (200 - 2000 µm) prepared for settling are likely to be ruptured under moderate velocity gradients occurring in flocculation tanks, whereas smaller agglomerates (< 200 µm) may withstand strain forces much higher than found under practical conditions. An example of model application shows the particle stress in the entrance to porous media filters where typically high strain gradients may easily lead to a break-up of flocs larger than 200 µm.     

Probleme bei Planung und Betrieb von Absetzbecken für Straßenabwässer

Sedimentation basins are incorporated into runoff infiltration systems and serve as a retention system, in which the sedimentation of particles occurs as a result of gravitational force. The effectiveness of sedimentation basins in terms of removing particles is highly dependent on design parameters such as their dimensions and drainage times. To evaluate the flow distribution within sedimentation basins, a conceptual model was developed using a tracer and compared to the actual condition at the treatment system. Here, a significant difference in the height of the connecting tube between settling basin and filter basin was found. This leads to a drying out of the basin, which significantly affects the flow rates and hence the sedimentation there. Based on a model experiment with colour tracer, the flow paths were visually represented in the basin, and both the concrete variant and the effects of internal structures were considered. It was found that the incorporation of a baffle led to an improved utilization of the basin, and to water being retained for longer times. Due to the lower flow rate and these longer times, fine and medium-sized sediments could be easily settled. In a field study, the performance of a sedimentation basin for the removal of particles was evaluated based on the influent and effluent concentrations of total suspended solids (TSS). The street runoff treatment plant was monitored for one year and results showed that there was no particle accumulation in the sedimentation basin (there was no permanent retention of the particle loads). The mean TSS concentrations were 89 mg/L at the inlet of the sedimentation basin and 94 mg/L at the end of the settling tank, respectively. The structural design and operation of the system showed higher flow and turbulent flow conditions in the sedimentation basin, in which settlement of fine and medium sized particles was very low; as a result, the soil filter basin was loaded with runoff particles. Thus the particulate matter had to be removed either on the surface of the filter basin or within the porous space of the filter. The build-up of such particles can result in a significant increase of head loss due to clogging; therefore, filters must be maintained by removing the accumulated particles on a regular basis.     

城市水文模型原理刘家宏

城市水文过程因强烈的人类活动影响而发生了深刻变化,科学精细地模拟城市区域的产汇流过程是解析城市水问题机理的科学基础。在系统剖析城市水文模型原理的基础上,将城市复杂下垫面根据其透水特性划分为不透水单元、透水单元、半透水单元、伪透水单元、强透水单元、水域单元等六类基本单元,并构建了不同类型城市水文响应单元的水文特性曲线,基于圣维南方程组和Navier-Stokes方程提出了城市管网与河湖水系水动力学模拟的技术方案。在耦合城市水文响应单元的降水—截留—蒸发—入渗—产流模块、地表汇流模块、管网汇流模块、水系一维水动力学模块等基础上,以水循环过程为主线,将水文模型的径流输出作为城区一维管网、河道水动力模型的输入边界,实现水文模型与一维管网、河道水力学模型的集成。将单元水文模型通过城市管网和河湖水系等连接方式集成到城市水文模型系统中,弥补了现有城市雨洪模拟在水文学机理上的不足,可为城市排水防涝和海绵城市建设提供科学基础。     

一种塑料模型沙运动特性试验

对一种复合塑料模型沙的水下休止角、群体沉速、起动流速等运动特性进行了试验研究:使模型沙在静水中自然落淤成丘,通过几何关系可得水下休止角;将沙样按粒径分组进行单颗粒沉速试验,统计平均后再按质量加权得到模型沙群体沉速;在玻璃水槽中对5种水深下的泥沙起动流速进行了测量及经验公式验证。试验结果表明:该模型沙水下休止角为28.4°,较传统塑料沙、水下休止角范围大,具有较好的水下成形特性;对于该模型沙,其单颗粒沉速用W.W.Rubey公式计算精度较高,但群体沉速用中值粒径进行经验计算则精度不够,合理的代表粒径有待进一步研究;起动流速比传统塑料沙大,这与水下休止角试验是相符的,通过调整沙莫夫系数K,沙莫夫公式可较好地表述个别起动和少量起动的情况,大量起动时则不够精确。     

平原感潮河网区域城市洪涝分析模型研究

为开展平原感潮河网区域城市的洪涝分析,综合考虑了该类型区域河流密度大、具有城市的特殊下垫面以及市政排水对洪涝的影响等特点。以城市主干河流、堤防等交汇包围的区域为单元提出了河网排涝单元模型,以排水分区为单元按照其排水能力建立了排水概化模型,并与模拟主干河道和道路、模拟地面的洪水演进模型耦合,建立了平原感潮河网区域城市洪涝分析模型。以上海市浦西防洪保护区为例,开展了上游河道洪水、风暴潮及区域降雨和防洪工程调度综合影响下的洪涝分析。结果表明,黄浦公园等站潮(水)位过程与实测基本一致,苏州河、淀浦河、西大盈港等河流发生漫溢,与实际情况基本相符。研究成果对平原河网地区城市洪涝模拟具有参考价值。     

不同暴雨与城市化程度情景下城区内涝SWMM模拟分析

将郑州市某区域在不同暴雨重现期、不同城市化程度、不同排水管径等情景下应用SWMM模型进行内涝模拟研究。结果表明城市内涝与城市扩张和排水管网布置等有密切关系。其重现期为2年、10年和100年时,开发后82%不透水面积比例的径流总量分别是开发前39%不透水面积比例的2.5倍、1.8倍和1.3倍,该水文效应在短重现期降雨条件下更为明显。研究结果可为城市发展规划与管网布置提供相应的技术支持。     

基于SWMM的城市洪水内涝模型研究

城市化程度的提高,直接改变了城市暴雨径流形成条件,使其雨洪运动特性发生了较大变化,城市防洪排涝问题日益严峻。文章以SWMM模型为基础,结合澳门大学横琴岛校区的实际资料模拟地面的溢流过程,并对造成溢流的可能原因地面不透水面积所占比例、管道粗糙度和管径进行量化分析比较,为城市土地规划利用和排水管网设计提供依据,有效减轻城市洪水内涝灾害。     

泥沙颗粒生长生物膜后沉降的实验研究Ⅱ：沉降速度计算

泥沙生长生物膜后相应的物理特性会发生改变。本文主要探讨泥沙颗粒在微生物生命活动的影响下沉降特性的改变情况。将官厅水库的泥沙分为6组,使用天然水和营养液的混合液对泥沙进行培养,用来模拟富营养水体中泥沙颗粒特性的发展变化情况。对于生长生物膜后的絮体颗粒在各个不同培养时间的沉降运动,实验采用先进的图像采集观测系统进行拍摄采样,并利用图像分析测量颗粒大小和沉速的变化,推导了生长生物膜后的颗粒沉速计算公式。研究表明生物膜极大地改变了颗粒的表面特性,使得颗粒下沉阻力增大,与同等大小无生物膜黏连的泥沙颗粒相比沉速明显减小。     

泥沙颗粒生长生物膜后沉降的实验研究(Ⅱ)——沉降速度计算

泥沙生长生物膜后相应的物理特性将会发生改变，本文主要探讨泥沙颗粒在微生物生命活动的影响下沉降特性的改变情况。通过将官厅水库的泥沙分为六组，使用天然水和营养液的混合液对泥沙进行培养，用来模拟富营养水体中泥沙颗粒特性的发展变化情况。对于生长生物膜后的絮体颗粒在各个不同培养时间的沉降运动，实验采用先进的图像采集观测系统进行拍摄采样，并利用图像分析测量颗粒大小和沉速的变化，推导了生长生物膜后的颗粒沉速计算公式。研究表明生物膜极大的改变了颗粒的表面特性，使得颗粒下沉阻力增大，与同等大小无生物膜粘连的泥沙颗粒相比沉速明显减小。     

河湖淤泥絮凝沉降特性试验研究

絮凝沉降性能是河湖疏浚淤泥资源化处理中重要且未完善的研究课题。以武汉沙湖、官桥湖及南湖3种淤泥为研究对象,通过沉降筒试验,利用清浑交界面沉降速度和上清液浊度研究了粒径分布、初始含沙量及高分子聚合物对河湖淤泥絮凝沉降特性的影响规律,并探讨了沉降筒尺寸对试验结果的影响。试验结果表明:河湖淤泥粒径越小,淤泥絮凝沉降越慢,上清液浊度越小;随初始含沙量的增加,河湖淤泥整体沉降速度变小,但当初始含沙量增加到一定值后,初始含沙量的影响作用开始变弱;高分子聚合物会促进河湖淤泥絮凝沉降;沉降筒尺寸虽然对试验结果略有影响,但对于分析河湖淤泥絮凝沉降特性无较大影响。研究河湖淤泥絮凝沉降特性对于河湖通航、蓄洪、水质修复、疏浚淤泥的处理均有重要意义。     

城市洪涝仿真模型地下排水计算方法的改进

为了增强对城市地下排水的模拟能力,获取更为详细的计算结果信息,提高城市洪涝分析水平,对现有洪涝仿真模型的地下排水计算进行了改进,提出在同一模型中对排水管网采用简化和细化相结合的计算方式。简化计算采用等效体积法实现,细化计算采用建立真实管网的一维动力波方程实现,并在特殊道路通道和网格上实现地上、地下水流交换。同时,在降雨产流计算中考虑地面透水性,形成了面向城市降雨产、汇流和排水的洪涝全过程模拟模型。改进后的模型对地下排水的模拟适用性更强,计算结果更为丰富,提高了区间暴雨导致的城市洪涝模拟能力。文中以上海市蕴南控制片洪涝分析计算为例,说明改进模型可获得较好的应用效果。     

石英砂加载混凝工艺的DOM去除特征与混凝机理

为处理未纳入管网的市政污水,采用石英砂加载混凝工艺,考察石英砂的粒径及其投加量对处理效能的影响,分析了溶解性有机物(dissolved organic matters,DOM)的去除特征,并探讨了石英砂加载混凝机理.结果 表明,与常规混凝相比,当石英砂的粒径和投加量分别为200目和1.0 mg/L时,石英砂加载混凝工艺...